Influenza Pandemic swept the world from 1918 to 1920 taking between 50-100 million lives.

The influenza was named Spanish Flu for two reasons. Firstly because Spain was highly affected by the flu in the early stages of the pandemic and secondly because despite being a neutral country in the World War 1, they took little care about stopping the flu so the most accurate reports about the flu came from Spain

The 1918 flu pandemic struck in three waves across the globe, starting in the spring of that year, and is tied to a strain of H1N1 influenza ancestral to ones still virulent today.

 In Pennsylvania, the influenza epidemic began almost unnoticed in the middle of September. First a few cases, and then the numbers began to rise rapidly. Worried state health authorities decided to add influenza to the list of reportable diseases. Their concern increased when 75,000 cases were reported statewide. The worst was still ahead.

A viral infection of the respiratory passages known as influenza, or flu, may be accompanied by symptoms of fever, chills, headache, muscle ache, sore throat, and weakness. It is spread by breathing airborne droplets infected with one of three influenza viruses—A, B, or C. The incubation period is two to three days. In general, type A is more debilitating than type B, and type B more than type C. Since type C causes only minor illness, it is sometimes mistaken for a common cold. A person who has type C virus becomes immunized against type C for life. A person infected with a strain of type A or type B becomes immune to that strain but is still susceptible to infection with new strains of the virus. New forms of the type A virus arise throughout the world.